spark plug hole repair

[JPark]

I think I'm going to be having to do a plug thread repair, and it's better to do it before it leaves me stranded. It's come loose on me twice and I don't think it's from under tightening, although I'm pretty conservative on torque.

Is there any consensus on what type of repair is best on a Hodaka? Helicoil is pretty common, but I'd rather see a steel insert for a half inch reach plug [B8H] if such a thing exists. Never had much confidence in 3/8" plugs in aluminum.

Open to any and all suggestions.

[thrownchain]

Why not source a different head? What motor?

[JPark]

100B+ motor. Only head I have. No homeless heads around here, and I have access to a free machine shop/welding service. I'm just interested in making it better than stock if I can.

[Bruce Young]

Jpark, like thrownchain suggested why not source out a replacement head, you did not indicate what model of machine you need the head for. There are hundreds of good used heads and cylinders and old motors laying around the Hodaka World, you just need to tell us what eng. you need the items for and you might be surprised what someone will offer, "just pay the freight and its yours", "just ask". Hodakapartsidaho.com

[taber hodaka]

I would use a used head or have it al welded and machined. works well just don't over torque. I never dad good luck with the steel repair coils. -------------------------------- Clarence

[matt glascock]

What Clarence said. If you have access to a high-quality aluminum weld shop that can perform the mill work, that's the best way to go. That Helicoil in a cylinder head will get pounded about a quarter-million times per hour of running time and be subject to quite a shock load at each power stroke. That's asking a lot. I think I have at least a few Ace heads in my parts stash. I can do a little digging and if I have one that is in decent shape, I will send it to you, postage paid, for a $20 donation to the Hodaka Club.

[viclioce]

Way to go Matt!!! Victor

[Droydx]

I have a head that I had repaired with a helicoil. When I did a pressure test on the assembled engine, I found that it leaked pressure through the repair...Not sure if it was enough to make any kind of difference on a stock 100B+ but I ended up using another head that hadn't been repaired.

Andy

[matt glascock]

Thanks Victor. Just paying it forward (like you've done many times).

[JPark]

Thanks for all the replies so far. As I suspected, the helicoil doubles the thread interface and, despite the spark plug gasket, can leak and shuffle and wear. There isn't a lot of metal there to use an insert.

I'm leaning towards making a shouldered aluminum plug and welding it in. Then I'd like to go to a D8E plug - 12mm X 19mm - which, due to less area, has a lot less force on it and lots more threads to spread it over. Once you get over the size in the hand, they actually function just as well and I could argue that the shorter ground electrode is a plus.

Sure, my favourite plug is a BE size and the DE takes an 18mm plug wrench [?? why not 19mm or 17mm?], but I can deal with that. Is there an acronym for WWTT - what were they thinking?

This all reminds me of Czech racer that I worked with back in 1970 whose CZ blew its spark plug out in practice. I took some aluminum foil from the luchbox and wrapped it around the plug and put it back in, and it held. Toward the end of the race season I asked him what he had done to repair the hole and he said he just replaced the foil whenever he had the plug out and was getting a new bike for next season anyway.

Moral of story? Keep some aluminum foil in in the toolkit.

[JPark]

And Matt; thanks for the offer.

[Al Harpster]

JPark

If you decide to proceed as you've outlined please take pictures as you progress & post them.

[JPark]

My machinist prefers not to weld. Instead, he plans to make a shouldered aluminum plug threaded to 5/8" fine and make it slightly longer than the hole so he can stake the protrusion to keep it from loosening. This gives about 2mm of material outside the plug thread for stability. He's done it before, and this way the insert could be removed by cutting back the staked bit.

If you had the insert, a 9/16 bit and drill press and a 5/8" fine tap you could do it pretty quickly. The DE size plug makes more sense in aluminum than a - no bovine inferences, please - BS size. The insert being the same expansion rate with no welding stresses looks pretty permanent to me. No change in heat transfer either.

If I just rode the bike occasionally I'd just helicoil it but this bike will be used a lot. The machine shop is in the process of moving to larger premises so it will be a few weeks until I get around to it. I'm not down to aluminum foil yet...

I tried taking the plug cap off the wire assuming that it is a screw on and it doesn't want to come off. Were these bonded on? Is the wire solid core? I could just cut it off and screw on a D size but don't want any surprises.

[bobwhitman]

JP
As already suggested, please take pix, notes and send me a write up as you do this for the resonator!
[email protected]

[JPark]

Will do, Bob. I notice you're in Eugene; I have friends there and really enjoy the area.

There must be a way to put location in your signature. I find it nice to know the location of the posters, just for context, but it doesn't seem to be obvious to an E dummy like me. ?

[TheBevman]

I've successfully heli-coiled a few Ace 100 heads. The kit was from my local auto parts store.

Here's a link for a similar:
https://www.oreillyauto.com/detail/b/he ... 8699?pos=5

The insert has spikes around the top portion of it. Once installed, there's a sized, shouldered drift that is used to force the spikes into the head to lock it. I used red Loctite and haven't had a problem or an air leak yet.